MONITORING POWER-RELATED PARAMETERS IN A POWER DISTRIBUTION UNIT
A power distribution unit (PDU) disposable in an electrical equipment rack. The PDU has a housing, a power input penetrating the housing, outlets in the housing, a processor disposed in the housing, voltage and current sensors, and a voltage calculation procedure communicable with the processor. The processor samples voltage and current waveforms and calculates RMS values and other power parameters. A method of managing electrical loads each drawing electrical power from a PDU includes repeatedly sampling voltage across and current flowing through each of the loads, calculating raw RMS values of voltage and current, and scaling the raw RMS values to obtain corrected RMS voltage and current values and other power parameters.
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This application is a continuation of U.S. patent application Ser. No. 13/686,685, filed Nov. 27, 2012, titled “MONITORING POWER-RELATED PARAMETERS IN A POWER DISTRIBUTION UNIT”, which is a continuation of U.S. patent application Ser. No. 12/717,879, filed Mar. 4, 2010, now U.S. Pat. No. 8,321,163, issued Nov. 27, 2012, titled “MONITORING POWER-RELATED PARAMETERS IN A POWER DISTRIBUTION UNIT”, which claims priority to U.S. Provisional Patent Application No. 61/157,546, filed Mar. 4, 2009, titled “SYSTEMS AND METHODS FOR MONITORING POWER-RELATED PARAMETERS IN A POWER DISTRIBUTION UNIT”, the entire disclosures of each of which are incorporated in their entireties herein by reference.
BACKGROUNDPower monitoring and metering have long been used in some applications to provide any of a number of items of information to different entities that supply, deliver, and consume power. One common use of such information is to determine energy consumption for purposes of billing a user for the power received by that user. Centralized computing facilities, often referred to as server farms or as data centers, continue to house more and more computing equipment. Such facilities often have numerous individual pieces of computing equipment arranged in racks. Power Distribution Units (PDUs) have long been utilized to supply power to racked electronic equipment in such facilities and in other kinds of facilities as well.
A conventional PDU is an assembly of electrical outlets (also called receptacles) that receive electrical power from a source and distribute the electrical power to one or more separate electronic appliances. Each such unit has a power cord plugged in to one of the outlets. PDUs also have power cords that can be directly hard wired to a power source or may use a traditional plug and receptacle connection. PDUs are used in many applications and settings such as, for example, in or on electronic equipment racks. A PDU located in an equipment rack or other cabinet, together with other devices connected to the PDU such as environmental monitors, temperature and humidity sensors, fuse modules, or communications modules that may external to or contained within the PDU housing may be collectively referred to as a Cabinet Distribution Unit (CDU).
As mentioned, computing facilities generally include electronic equipment racks, such as standard RETMA racks, that commonly comprise rectangular or box-shaped housings sometimes referred to as a cabinet or a rack and associated components for mounting equipment, associated communications cables, and associated power distribution cables. Electronic equipment is commonly mountable in such racks so that the various electronic devices are aligned vertically one on top of the other in the rack. Often, multiple such racks are oriented side-by-side, with each containing numerous electronic components and having substantial quantities of associated component wiring located both within and outside of the area occupied by the racks. Such racks commonly support equipment that is used in a computing network for an enterprise, referred to as an enterprise network.
In many cases, computing facilities such as server farms or data centers support large networks, referred to as enterprise networks. Enterprise networks exist to support large world-wide organizations and depend on a combination of technologies, e.g., data communications, inter-networking equipment such as frame relay controllers, asynchronous transfer mode (ATM) switches, routers, integrated services digital network (ISDN) controllers, and application servers, and network management application software. Such enterprise networks can be used to support a large company's branch offices or campuses throughout the world, and, as such, these networks have become mission critical to the functioning of such organizations. Masses of information are routinely expected to be exchanged, and such information exchanges are necessary to carry on the daily business of modem organizations. For example, some international banks have thousands of branch offices placed throughout Europe, Asia and North America that each critically depend on their ability to communicate banking transactions quickly and efficiently with one another and with their respective headquarters.
A typical enterprise network uses building blocks of router and frame relay network appliances mounted in equipment racks. Such equipment racks are distributed to remote point of presence (POP) locations in the particular network. Each equipment rack can include frame relay controllers, routers, ISDN controllers, servers and modems, etc., each of which are connected to one or more power sources. The value of POP equipment can range from $200,000 to $500,000, or higher, and the number of individual devices can exceed a thousand.
Many equipment racks may be located in a data center. One or more such data centers may serve as data communication hubs for an enterprise. On the other hand, more than one enterprise may use computing facilities in a data center. Existing network management systems provide relatively little information representing the status of a data center or of racks or individual components in the center.
SUMMARYBriefly and in general terms, aspects of the invention reside in a power distribution unit having a power input, a voltage sensor for the power input, a plurality of power outputs connectable to electrical loads, a current sensor for each output, and a power monitoring section. The power monitoring section receives signals from the sensors and samples the signals to obtain samples of voltage and current during a cycle of input power, calculates raw RMS values of voltage and current, and scales those values according to a predetermined calibration factor to obtain corrected RMS voltage and current values for one or more of the loads.
The power monitoring section may also calculate other power metrics for the loads such as average active power, average apparent power, power factor, input current crest factor, phase angle between voltage and current, and energy consumed over time. The energy consumed may be expressed in kilowatt-hours.
In some embodiments the foregoing components are all installed in a cabinet PDU housing.
In some embodiments the power monitoring section includes an analog-to-digital converter (ADC) that receives signals from the sensors and converts those signals to digital form, processing logic that receives the digital form of the signals, and a memory that may store the converted ADC digital signals as well as any of the power metrics over one or more cycles of input power.
The processing logic may compare samples of voltage and current over different cycles, or samples during a cycle may be compared with pre-stored model samples. In either comparison, if differences exceed a predetermined magnitude, an alert signal can be generated.
In some embodiments a timing sensor detects zero crossings of input voltage cycles. This information is used to calculate input voltage frequency. The zero crossing information may also be used to calculate a reload value that determines input power signal sampling intervals.
Power metrics and alert signals may be transmitted through a communication section to a remotely-located network power manager.
A power distribution unit according to some embodiments includes a power distribution unit housing disposable in an electrical equipment rack of the type in which a plurality of electrical components are removably mountable. A power input penetrates the housing and a plurality of power outputs are disposed in the housing. A processor is also disposed in the housing and is communicable with a voltage calculation procedure which may for example be an RMS calculation procedure. A voltage sensor is communicable with the power input and the processor, and a plurality of current sensors are communicable with one of the power outputs and with the processor.
Aspects of the invention reside in a method of managing a plurality of electrical loads drawing power from a power distribution unit. The method includes sampling voltage across and current flowing through each of the loads repeatedly during one cycle of input power, calculating raw RMS values of voltage and current from the samples, and scaling the raw RMS values according to a predetermined calibration factor to obtain corrected RMS values.
The foregoing is a brief description of various aspects of various exemplary embodiments. The scope of the invention is to be determined by the claims as issued and not by whether given subject matter includes any or all such aspects, features, or advantages or addresses any or all of the issues discussed in the foregoing.
In addition, there are other advantages and varying novel features and aspects of differing embodiments. The foregoing and other features and advantages will become more apparent from the following detailed description, which proceeds with reference to the accompanying figures.
Several embodiments including the preferred embodiments and currently known best mode of the present invention are shown in the following description and accompanying drawings in which:
Exemplary embodiments of power distribution, monitoring, and management systems are described herein. The present disclosure provides exemplary embodiments with capability to determine the power being delivered to a power distribution apparatus and the power being delivered from the power distribution apparatus to one or more electrical loads. This facilitates efficient determination of power usage for various different components that are associated with a facility, and therefore provides an ability to manage power to the various different components. In many cases, numerous PDUs and CDUs may be located in a facility, with each supplying power to several different electrical loads. Knowledge of power being delivered to various equipment in a facility may be used to evaluate, improve, and manage power consumption in a facility and across multiple facilities, such as data centers.
In various embodiments, systems and methods are provided that sense and output information related to current and voltage provided to various different components and applications powered by one or more PDUs or CDUs. The current and voltage information may be used to provide any of several measurements, referred to as power metrics, such as one or more among the following: power consumed by each component, power factor, crest factor, true RMS current and voltage measurements, active power, apparent power, and energy consumption.
One or more such metrics may be used for a number of purposes, such as for analysis and actions that enhance the efficiency of components that are receiving power, enhance the efficiency of a group of components that are receiving power, enhance the efficiency of a data center, and enhance the efficiency of an enterprise network. Metrics also may be used, for example, to provide information related to management of assets in a computing network, accurate tracking and billing of energy used by assets, and identification of components that are receiving or providing power in an anomalous manner indicating a malfunction or potential malfunction, to name a few examples.
Some embodiments of the present disclosure described in more detail below provide, alone or in combination, one or more advantages over traditional PDUs. In certain embodiments, a PDU has an integrated AC input clock solution, in which a power monitoring circuit or a power meter does not require an external oscillator to provide a time base. Some embodiments may receive the incoming AC waveform to synchronize the internal microprocessor clock to an AC cycle and provide power metrics that are timed to AC cycles to provide accurate measurements. Such a solution can, in certain embodiments, further provide a relatively low cost solution by reducing components, as well as a corresponding reduction in the area required and power used, for performing power monitoring and metering.
Some embodiments include power monitoring and metering circuits that may be used in a number of different applications, such as within a PDU, within a switched-mode power supply, and within commercial and residential power meters, to name a few.
Some embodiments provide predictive failure of various power components. A digitized version of the AC power waveform of a component can be used to identify anomalies in the waveform and thereby flag potential problems with the component. Also, the power being supplied to an individual component can be monitored and used as a basis for identifying abnormal operation of that component.
Some embodiments provide an accurate energy accumulation scheme for one or more outputs associated with a single power monitoring and metering circuit. Voltage or current may be sampled during an AC cycle, and in this regard in some embodiments both voltage and current are sampled nearly simultaneously for an output.
In some embodiments, the product of each of the samples can be summed over the AC cycle. An AC cycle may be sampled at a pre-determined frequency. At each sample interval a single AC cycle is sampled at a much higher sample rate (both voltage and current) to provide the power information which is then accumulated at the lower waveform sampling frequency to provide energy measurement. For example, a predetermined sampling frequency of once every 24 cycles may be used. Such sampled cycles may be scaled and accumulated over a time period to provide an accurate energy measurement (the energy may be expressed in watt-hours) for each output.
In some embodiments, the invention provides a PDU in which one more outputs of the PDU may be switched to provide or remove power to a particular output. In some embodiments, a relay circuit has two transistors, one that initially switches the relay and a separate transistor for holding the relay with lower current draw. The second transistor is switched on a predetermined time following the initial relay turn-on, and subsequently the first transistor is turned off, thus providing a lower current flow through the relay coil. This arrangement uses less power than a switching transistor that holds the relay active. The resulting accumulated savings for numerous PDUs in a facility or network can be significant in certain applications. Such reduced power requirements may also generate less heating related to power consumption and may also enhance the lifetime of such components as compared to implementations not having such reduced power requirements.
Some embodiments having switched output capabilities can provide output switching at or near zero voltage or current crossings of the AC cycle or at least likely below the peak voltage or current in the AC cycle. In some embodiments, for example, the AC waveforms provided to an output are sampled at or near the point of zero current or voltage crossings and outputs may be switched at or near these zero crossings. In embodiments in which relays switch outputs, at or near zero voltage or current crossing can be less stressful on the relay and the relay points. This may result in increased component lifetime and reduced in-rush current into the component that receives power from the respective output to possibly also reduce stress on that component.
Some embodiments of the disclosure provide a modular construction of an outlet assembly with options to provide switched outputs or non-switched outputs, and the ability to determine if lack of power at an outlet is the result of loss of input power or a blown fuse.
Certain embodiments provide a multi-outlet power meter that monitors the voltage and current delivered to one or more power outputs. A monitoring circuit may include a voltage input having an analog-to-digital converter that samples the incoming voltage and provides a digital representation of the incoming voltage waveform. A current input for each power output, connected to the meter, has an analog-to-digital converter that samples the current input and provides a digital representation of the incoming current waveform. The samples of each of the current and voltage waveform may be collected to provide power metrics such as, for example, RMS voltage, RMS current, active power, apparent power, energy, power factor, and crest factor. This information is transmitted from the meter toward network components that may then report the information to a remote user.
In some embodiments, the systems may reveal when one or more components of a power distribution unit, or components that receive power from the power distribution unit, develop an abnormal current or voltage characteristic. Such identification may provide an indication of a potential failure of the component. In some embodiments, current and voltage information are collected for a component and compared against model or historical information. In the event that an anomalous event is detected, a message may be transmitted indicating the same such that an investigation or corrective action may be taken.
In some embodiments, information provided by PDUs or CDUs may be used by an organization to take action such as, for example, corrective action, improving the efficiency of operations, providing power metrics for specific components, providing more accurate billing for energy usage, or identifying equipment that may be a candidate for consolidating operations. In some embodiments, corrective action may be taken such as in the event that a CDU or PDU generates a warning that the current or voltage waveforms of for example, a power supply have a significant deviation from a historical or model waveform. In some embodiments, such deviations may indicate the power supply is malfunctioning and corrective action can be taken. In some embodiments, power metrics may be used to evaluate the operations of different items or groups of equipment to identify areas where efficiency can be enhanced, for example. Similarly, power metrics may be used to determine energy usage, and provide billing for separate pieces of equipment within a rack, for example. Furthermore, power metrics also may be used to identify multiple equipment, such as two servers, that are being used to service an application where utilization of the equipment is such that the operations may be consolidated and one or more pieces of equipment idled or placed in stand-by mode.
Individual equipment may be measured in order to determine various types of information related to power efficiency metrics. In embodiments described herein, power-related information is determined for various types of equipment, and this information provided to determine power usage related to that equipment. In some embodiments, a PDU is provided that senses and outputs the power used by various different components, including monitoring both the input power of the PDU and the power output to various components powered by the PDU. For example, to determine total computing equipment power (Power is (Volts×Amperes) or Watts) delivered by the PDU, the PDU could measure Watts for each input cord to the PDU(s), or the input power at various subcomponents that provide power to one or more pieces of computing equipment. The sum of all the power output to pieces of equipment measures the total computing equipment power delivered by the PDU and consumed by the computing equipment assuming all computing equipment assets are plugged into a PDU having the ability to measure power. In some embodiments, several metrics are calculated for each outlet in a PDU including voltage (true RMS Voltage), current (true RMS Current), active power (Watts), apparent power (VA), energy (Watt-hours), power factor (unitless), and crest factor (unitless). Each of these metrics may be used alone, or in combination with other of the metrics, to provide information related to components that are receiving power from the outputs of the PDU.
In other embodiments, an individual piece of computing equipment efficiency may be determined using one or more of computed metrics, such as MIPS/Watt. MIPS (million instructions per second) is a measure of the speed of execution of a processor. Thus, performance efficiency for a particular server, for example, may be measured or a cumulative efficiency calculated for all equipment in a data center. In embodiments that provide such metrics, the metrics may be provided for each outlet in the PDU, or for a subset of outlets in the PDU. The MIPS value of a component may be read over a network, for example, from the BIOS of the component, and combined with power metrics to provide a measure of performance efficiency. The sum of all the ‘per outlet Watts’ on a PDU may be used to measure the PDU's efficiency when compared to the input cord power to the PDU. In some embodiments, an individual piece of equipment may receive operating power from multiple power supplies. In such embodiments, the outlets that provide power to the piece of equipment are grouped using an application external to the monitoring circuit, with metrics from each outlet in the group summed to provide the corresponding metrics for the specific asset that is acquiring it power from multiple PDUs, CDUs, or multiple power supplies. Other embodiments provide the ability for an expense charge for the power consumed by each specific asset, and each outlet may record the amount of power used (Watt-hours) in the same manner as a utility meter.
With reference now to
The PDU 20 of this embodiment includes a power supply 32. It also includes a network interface card (NIC) 34 that has application firmware and hardware that allows the PDU 20 to communicate with other modules within a CDU, and in this embodiment includes a power manager agent application 36. The PDU 20 includes a plurality of power outlets 40 arranged within an intelligent power module (IPM) 44. The NIC 34, and power manager agent 36 are connected to the computer network 24. The intelligent power module 44 controls the application of power from the input power to a corresponding power outlet among the power outlets 40, and is in communication with the power manager agent application 36 to provide power and power cycling on-off for one or more of the corresponding power outlets, which may be accomplished through one or more relays 45 and associated relay driver 46. The IPM 44 receives input power, and provides power to one or more outlets 40 through the relays 45. The IPM 44 may also provide power state sensing or load sensing with respect to the corresponding power outlet in response to one or more commands. The IPM 44 in this embodiment includes a microprocessor 48 used to control the power applied to a corresponding power outlet. The microprocessor also is connected to a voltage sensing device 52 and a current sensing device 56 to sense the voltage and current at corresponding individual power outlet(s). The microprocessor 48 uses this information to determine the power supplied through an outlet, as will be described in more detail below. The microprocessor 48 also receives a power measurement from the input power supply 32 through an input voltage sensing device and an input current sensing device 21 internal to the PDU. In this embodiment, the IPM 44 also includes a power supply 58 used to provide DC operating power to components within the IPM 44. A display 23, for example a single- or multi-digit LED display, may be included to provide a visual indication of voltage, current or another power metric; the display is shown as communicating with the microprocessor 48 but could instead communicate directly with other elements such as the sensors 56 or 52. The display may instead by driven by either the NIC 36 or the power supply 32.
The network power manager 28 of
The power outlet module 200 also includes one or more line voltage sensors, each including a voltage dropping resistor network 224, and an opto-isolated operational amplifier 228 to provide instantaneous line voltage information to the power source 32. The line voltage may also be determined through various other configurations. The line voltage sensor, for example, may include a voltage sense transformer that provides isolation and allows voltage to be determined based on the voltage across the transformer and the turns ratio of the transformer. Other embodiments may not provide isolation, instead achieving isolation from high-voltages in other manners. The microcontroller uses the current information related to each of the respective outlets 202-216, along with the line voltage to calculate the power metrics associated with each of the individual outlets 202-216. This information may be communicated to other components through communications link 230 through, for example, a communications bus. One or more voltage sensors may be provided for each power input if the PDU has more than one, which would be the case for example if polyphase power is provided. Or a separate voltage sensor may be provided for each group of outlets or even for each outlet individually. Using multiple sensors may provide improved accuracy by avoiding the effect of any internal voltage drops in the wiring between the power input to the PDU and the outlets.
In one embodiment, the power outlet module 200 includes eight outlets (202-216) each of NEMA 5-20R type, contained in a housing. It will be understood that this embodiment, and other embodiments described herein as having NEMA 5-20R type outlets, are exemplary only and that any of various other types of outlets alternatively can be used. For example, the “outlets” can be other NEMA types (e.g., NEMA 5-15R, NEMA 6-20R, NEMA 6-30R or NEMA 6-SOR) or any of various IEC types (e.g., IEC C13 or IEC C19). It also will be understood that all “outlets” in a particular power outlet module 200, or other module-outlet described herein, need not be identical. It also will be understood that the “outlets” are not limited to three-prong receptacles; alternatively, one or more of the “outlets” can be configured for two or more than three prongs in the mating male connector. It also will be understood that the “outlets” are not limited to having female prong receptacles. In any “outlet,” one or more of the “prong receptacles” can be male instead of female connection elements, as conditions or needs indicate. In general, as used herein, female and male “prong receptacles” are termed “power-connection elements”. Furthermore, the principles described herein also are applicable to devices that may be hard-wired into an outlet module. While outlet module 200 of this embodiment includes eight outlets, it will be understood that this is but one example and that an outlet module may include a different number of outlets.
The housing for an outlet module may be any suitable housing for such a device, as is known to one of skill in the art, and may be assembled with other modules in a CDU. Such a housing generally includes a front portion and a rear portion, the front portion is substantially planar, and the rear portion is substantially planar and parallel to the front portion. The housing also includes longitudinally extending side portions and transverse end portions. The front portion, rear portion, side portions, and end portions are generally orthogonal to each other in a generally rectangular or box-type configuration. The housing can be made of any suitable, typically rigid, material, including, for example, a rigid polymeric (“plastic”) material. In at least certain embodiments, the front and rear portions are made from an electrically insulative material, whereas in other embodiments conducting materials are used for safe ground bonding. The side portions and the end portions may be integrally formed, optionally along with the front portion or the rear portion. Furthermore, while the outlet module described in this embodiment includes a housing, other embodiments may include an outlet module that does not include a housing. For example, an outlet module may include a number of outlets coupled together with no exterior housing that may then be installed into another piece of equipment.
Each outlet 202-216 is interconnected to the power source 32 through any of a number of well known connection schemes, such as spade, lug, plug connectors, screw connectors, or other suitable type of connector. Furthermore, if desired, one or more of these electrical connectors can be located inside the housing or outside the housing, in embodiments where the power outlet module includes a housing.
The microcontroller 220, in this embodiment, receives current information for each outlet 202-216, along with voltage information and calculates various power-related metrics for each outlet, with this information reported through the communications link 230. For example, the power per outlet is determined by multiplying the instantaneous voltage by the instantaneous current for a particular outlet, and integrating this product over time to give energy used (kilowatt hours, etc.) Examples of several metrics will be discussed in more detail below.
With reference now to
In this embodiment, an outlet module includes eight (8) individual outlets organized into logical groups of four outlets each.
With continuing reference to
As mentioned, in some embodiments switched outputs are provided. With reference now to
Each relay 602-616 is connected to a relay driver circuit 678-692, respectively, that provide signals to switch the relays 602-616. The relay driver circuits 678-692 are electrically connected through a connection 696 to a microcontroller 904 (see
In such a manner, the power required to hold the relays 602-616 is reduced as compared to the power required to initially switch the relays 620-616 from open to closed. In one embodiment, the holding transistor requires about 75% of the power to maintain the relays 602-616 closed than would be present if a single transistor were used to both switch and hold. In embodiments where numerous switched outlets are present in a facility, such power savings can be significant in operating power reduction for the associated CDUs, which in turn reduces heating, allows for increased component density on a circuit board or within a housing, and also increases the lifetime of components. Other embodiments, however, may include different switching components as will be readily apparent to one of skill in the art.
With reference now to
As illustrated in
In the embodiment of
Line voltage measurements are provided, in this embodiment, through a voltage sensor circuit 800 that is illustrated in
An opto-coupler 824 is connected to the line input through a diode 814 and a resistor 815 and provides a frequency sense signal at an output 826 to indicate that AC line voltage is present at the Intelligent Power Module and also provides an approximately 50% duty cycle output that is based on the line frequency of the input power. Thus, for each AC cycle of the input power, the frequency sense signal will have a logical high signal for approximately one half of the AC cycle. The leading or trailing edge provided by the frequency sense signal provides an accurate measurement of the frequency of the input voltage frequency that may be used by a processing circuit to synchronize power metrics to an AC cycle.
In embodiments where all of the outlets of an outlet module are powered by a single power source, a single voltage sensor circuit 800 is used, and in embodiments where different outlets in the outlet module are supplied power from different power sources, a second voltage sensor circuit is provided for the second power input to the outlet module. As discussed above, this embodiment may be implemented using printed circuit boards that provide circuitry for various features described. In this embodiment, the voltage sensor circuit(s) are provided on the same printed circuit board as the current sensor circuit 710, although it will be readily recognized that other configurations may be implemented.
Referring now to
In this embodiment, the microcontroller 904 filters the current and voltage sense signals to reduce high-frequency noise that may be present. The digitized current sense signals are scaled for 16 Amps with a 2.5 crest factor, in this embodiment. The voltage sense signals(s) are received on voltage input channels. In embodiments having different power sources for some outlets, one voltage input channel per outlet group is provided. The voltage input channels are provided to a single-ended ADC input and a digitized output scaled for +/−390 volt peaks. The frequency sense signals for each power source are also provided to the microcontroller. The frequency sense signal(s), in some embodiments, is (are) used for frequency determination and timing of cycle sampling to provide accurate correlation of inputs to a particular AC cycle. The timing, in an embodiment, is auto-adjusted every second to compensate for inaccuracies, such as temperature drift, in the internal clock of microcontroller 904.
Use of the frequency sense signal 826 provides for accurate timing in the microcontroller 904 without the use of an external oscillator as an accurate time base. The ability to measure the frequency sense signal 826 provides enhanced accuracy for timing used in calculating power-related metrics for each outlet. In this exemplary embodiment, two signal types are digitized by an ADC within the microcontroller, the voltage and current signals. Synchronizing the sampling of both the voltage and current waveforms, utilizing frequency sense signal 826, provides for enhanced accuracy in the power-related measurements. It is well known that internal clocks in microcontrollers such as microcontroller 904 have some variability, such as plus or minus two percent. Such internal clocks are typically subject to frequency shift with changing temperature, and also have variability between different microcontrollers. In this embodiment, the frequency sense input allows for real-time compensation of the microcontroller internal clock variance to insure accurate sampling of the AC voltage and current waveforms. The voltage and current sense inputs on the microcontroller 904 are sampled nearly simultaneously 120 times per any AC cycle. The number of samples per cycle, 120 in this example, provides sampling of frequency content up to the 14th harmonic of a 50 or 60 hertz power input, allowing for measurement of real energy at harmonics present in a non-perfect sinusoid. The ADC, in an embodiment, within the microcontroller is a 10-bit ADC hardware, with four times over-sampling to provide an effective 11-bit ADC.
The computation of several power metrics will now be described, for an exemplary embodiment. In this embodiment, discrete samples are taken for one current and voltage channel for an AC cycle, which produces a digital measurement at each sample interval. After the samples are taken over one cycle, calculations are performed by the microcontroller, these calculations consume about one-and-a-half AC cycles in this embodiment. After the calculations are performed, the next channel is sampled beginning at the start of the next AC cycle. Thus, in this embodiment, there are three cycles dedicated to the first channel, the next three cycles dedicated to the second channel, and so on. Accordingly, in this embodiment with eight outputs monitored, each channel is sampled once every 24 AC cycles.
Also, voltage and current inputs are calibrated and provided to the microcontroller 904 in some embodiments. The current inputs, in an embodiment, are scaled to 16 amps at 2.5 crest factor and with the voltage input(s) scaled for 390 volts. Variances in the resistors and toroids, in an embodiment, is accounted for through calibration of the input channels. In one embodiment, the voltage and the current are calibrated based on active power and apparent power for each channel, although calibration based on other metrics may be used, such as calibrating the voltage and current individually. In embodiments that calibrate voltage and current individually, any errors that are in opposite directions will tend to cancel, and any errors in the same direction will be multiplied, when doing a power calculation. In embodiments that calibrate based on active and apparent power, the multiplied error may be reduced. The microcontroller 904, in this embodiment, also provides for calibrations to account for system phase error and provide near-zero to near-full-span voltage and near-zero to near-full-span current digitization.
With reference now to
With reference now to
The operational steps shown in
The procedures illustrated in
In one embodiment, the samples of voltage and current in a waveform are compared against a model waveform or a historical waveform for that particular channel, and any significant deviations from the comparison may be flagged as anomalous indicating that there has been a change related to the associated component. Such a change may indicate the component may not be operating properly, may be about to fail, or may have had a failure. For example, waveforms of the current drawn by a device and the voltage drawn by the device, when compared to historical or reference waveforms, may indicate a fault or other condition that should be investigated. For example, a switched-mode power supply located within a server that receives power from a PDU may be drawing power in a manner that indicates an imminent failure. Embodiments described herein provide the ability to assess the health of such power supplies in an installed base of power supplies in data center equipment racks without requiring any modification of the power supplies.
In some embodiments, currently sampled waveform information is only maintained in memory long enough to be utilized to generate and report the noted power metrics. Other waveforms, however, may be maintained in memory for comparison, such as in the form of or representative of one or more sample or reference waveforms or portions of one or more waveforms. In addition, the waveform information might be maintained in memory longer or otherwise stored for later use in, e.g., providing a basis for comparison. For example, when a system is initially set up and tested, the waveform may be stored and used for later comparison.
Referring again to
Also calculated is apparent power, which is the product of the RMS current and the RMS voltage calculated earlier, having units of volt-amps or VA. Power factor, the ratio of the active power to the apparent power, is calculated, which directly relates to the phase angle difference between the current and voltage. Power factor is calculated by taking the active power calculated from all the data points divided by the apparent power, which was the product of the RMS current and voltage. The next item calculated in this embodiment is current crest factor. The current crest factor is the ratio of the peak of the current waveform to the RMS of the current waveform.
Finally, energy is calculated. As mentioned above, embodiments are provided in which the microcontroller does not receive a time base from an external oscillator. The timing for such embodiments is based on cycles of the incoming AC waveform. As is well known, frequency of incoming AC power is generally 50 Hz or 60 Hz, depending upon location. Furthermore, most, if not all, industrialized nations have electrical generation and distribution systems that provide a relatively stable frequency of incoming AC power. The stability of incoming AC frequency may be used to provide a relatively accurate timing mechanism for starting and stopping ADC conversions. As described above, one embodiment samples eight channels over the course of 24 AC cycles. The relative accuracy of the incoming AC signal as a time base provides knowledge that there is an accurate measuring every 24th cycle for each channel with very little drift.
In an embodiment, the input power signal is sampled to determine if the input power is 50 Hz or 60 Hz. At 60 hertz there are 216,000 cycles in an hour, and at 50 hertz there are 180,000 cycles in an hour. With this information, and the measurement of one current channel every 24 cycles, energy may be calculated by multiplying the active power times 24, representing the total of all 24 cycles between measurements on a channel, and dividing by either 180,000 (at 50 hertz) or 216,000 (at 60 hertz). This provides a representation for power consumed by the channel during the 24 cycles. This energy computation is added to an energy accumulator associated with each channel. Each time the power for a channel is computed, the wattage use for the represented 24 cycles is added to the accumulator. In one embodiment, to reduce floating-point significance and rounding errors, when the accumulator (a floating point data type in memory) exceeds one, the accumulator is decremented and a double word integer associated with the channel is incremented to provide a number representing whole watt hours that have been measured for the channel. All of the values stored in memory may be reported through the communication interface to power managers or other applications that may then use this information to provide a number of different power-related metrics for components that receive operating power from the PDU.
As discussed above, relatively accurate timing is achieved in embodiments with a relatively high variability internal microcontroller clock though adjustments that compensate for inaccuracies in the internal clock. The compensation is achieved, in an embodiment, through providing the frequency sense input into an external interrupt pin on the microcontroller. The frequency sense signal, as discussed above with respect to the embodiment of
Once a positive edge is identified, then the first negative edge is identified. The interrupt within interrupt service routines for the external interrupt pin in the microcontroller is set to high priority to have relatively few, if any, interruptions from any other software interrupt service routines. When the first negative edge is detected, the microcontroller starts running a counter that counts every 12 clocks of the internal clock 912. In one embodiment, the internal clock 912 is nominally a 24.5 megahertz internal clock plus or minus 2%. The timer runs until the next negative edge is detected. Thus, regardless of the timing of the internal clock 912, a number of system clocks is determined that represents the span of time, from the microcontroller's view, of a single AC cycle. This number is converted into entire system clocks for an AC cycle by multiplying by 12, and then divided that by the number of samples collected within a single AC cycle (120 in this embodiment). Thus, a number of clocks is calculated that represents the time span for each sample of an AC cycle. This time is adjusted for expected interrupt latencies in the microprocessor, due to known entry and exit times in the interrupt service routines, etc., to generate a number of system clocks that represents the AC cycle. This value becomes a reload value for the timer that starts off each ADC conversion.
Thus, the timer becomes a time base for the digitizer of the ADC, and continues to be the time base for cycles when digitizing is not performed. Errors in the time base may accumulate over time. In one embodiment, errors are reduced by periodically re-measuring the number of system clocks in an AC cycle, such as once every five seconds. Such re-measuring provides adjustment to account for the actual speed of the internal clock, which is susceptible to temperature change, and also synchronizes the timer to a zero crossing of the voltage waveform. Such timing and synchronization of timers to an AC cycle provides relatively accurate power metrics. For example, if an external crystal time base were used, which is also susceptible to temperature change and variability of the incoming AC signal, errors can be introduced in between the timing of AC cycles and also synchronization to AC cycles. In the embodiments described here, the timer is re-synced to provide greater confidence that the samples used for RMS calculations are within the actual AC cycle. If RMS calculations are based on samples that begin after the cycle begins, or that end after the end of the cycle, error can be introduced to report either less or more energy than is being integrated. By re-syncing, sampling is more likely to be within a cycle and not outside the cycle, and thereby improves accuracy.
As mentioned above, to determine energy, an accurate measure of time is needed to provide, for example, a watt-hours number. The above description relies on the assumption of 50 or 60 hertz input signal being accurate. In some embodiments, the time as measured in the microcontroller is compared to time provided by a network controller to verify or adjust energy calculations. In one embodiment, the number of cycles counted in a timeframe of an hour is provided to a network card and compared to an actual real time clock view of an hour. In the event of any significant deviation, the network card may add a simple correction scale in for that. For example, if the microcontroller counts up number of clock cycles in an hour and reports to the network card, which measures 59 minutes, a simple adjustment may be made to the energy value.
In another embodiment, the timing of the AC cycles provides an indication related to when the incoming power waveform is at a zero-crossing. In this embodiment, the switching on and off of the relays (such as in
While described above with respect to a CDU, it will be understood that the power measurement circuitry and portions thereof have many applications beyond the exemplary embodiments described above. For example, a low-cost power metering circuit such as described may be incorporated into other equipment to provide information related to power parameters for the particular equipment. A server may, for example, include a power circuit as described to provide power-related information that may be used to assist in managing efficiency of the server by, for example, identifying that a server is not operating efficiently and that the load being serviced by the server may be a target to be moved to a different server. Similarly, it has been desired to have a switched-mode power supply that provides power-related information, but there is a strong desire to maintain as low a cost for these power supplies as possible. A single-chip solution without an external oscillator time base as described herein may provide a low-cost solution for incorporation into such power supplies. Further, such power metering may be incorporated into residential, commercial and/or multiple-unit power meters to provide power-related information for billing purposes.
With reference again to
As discussed above, the microcontroller 904 is interconnected to a communications bus (such as an I2C bus or SMBus). The microcontroller 904 reports over the bus, for each outlet/channel: (a) Voltage RMS (Vrms)—the pseudo-running-average of the eight most-recent Vrms values reported to a tenth volt; (b) Current RMS (Irms)—the pseudo-running-average of the eight most-recent Irms values reported to a hundredth Ampere; (c) Apparent Power (VA)—the pseudo-running-average of the eight most-recent VA values reported to in volt-amps; (d) Active Power (W)—the pseudo-running-average of the eight most-recent active power values reported in watts; (e) Power Factor (pF)—the pseudo-running-average of the eight most-recent pF values reported to a tenth; and (f) crest factor. This data may be received by an external system that collects the outlet information for which the data is provided, and used to determine metrics or provide information such as described above.
Those of skill will appreciate that the various illustrative logical blocks, modules, circuits, and algorithm steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware, computer software, firmware, or combinations thereof. To clearly illustrate this interchangeability, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware, software, and/or firmware depends upon the particular application and design constraints imposed on the overall system. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present invention.
For a hardware implementation, the processing units may be implemented within one or more application specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), field programmable gate arrays (FPGAs), processors, controllers, micro-controllers, microprocessors, electronic devices, other electronic units designed to perform the functions described herein, or a combination thereof. For a firmware and/or software implementation, the methodologies may be implemented with modules (e.g., procedures, functions, and so on) that perform the functions described herein.
A power management system embodying aspects of the invention is illustrated in
Similarly, a second equipment cabinet 2433 houses various components and one or more CDUs that provide power to these components. The system may include other equipment cabinets having more or fewer components or CDUs than depicted in the drawing.
The CDUs in the various cabinets communicate, for example through an Ethernet pipeline 2425 or through the Internet or some other suitable medium, with a server 2427. The server 2427 includes a database 2429 which may be stored in a memory, or on a magnetic disk or other medium. The database 2429 may be located in one place or distributed as desired. In some embodiments the server 2429 communicates with another system such as a Building Management System 2431.
As discussed previously, various electrical parameters respecting one or more of the outlets may be measured and used in managing power throughout the system. Current flow through each outlet, voltage present at the outlets, power factor, real and apparent power flowing through each outlet, phase angle between voltage and current at each outlet, accumulated energy for each outlet, power line frequency, and the like may all be measured and the measurements communicated to the server for presentation to a user or for preparing reports, generating messages, providing trends, and the like.
While embodiments discussed above describe exemplary implementations of components within an equipment rack or CDU, one or more of the principles, aspects, or features described above may be used in other applications. For example, generation of power metrics as described above, as well as internal clocking based on an incoming AC signal, may be incorporated in or with a power supply, such as a switched-mode power supply, to provide metrics related to the power supply or to otherwise use them or the underlying operation or information monitoring in association with the power supply or associated components or systems. For example, in this fashion such a power supply may monitor itself, take corrective or other action based on (in whole or in part) internal monitoring, and/or report out one or more power metrics. Such metrics may be used, for example, to anticipate power supply failure, measure power supply efficiency, and/or adjust the power supply to be more efficient for a given load.
With reference now to
A microcontroller 3030 receives an input from a toroidal current transformer 3040 associated with the high side AC power source. The output of the current transformer 3040 indicates the instantaneous magnitude of the current that is flowing through the input AC line, and may be configured such as the current transformers described above. The output of a voltage sense circuit 3050 is also received at the microcontroller 3030. The voltage sense circuit 3050 may include an isolating amplifier that amplifies voltage from a voltage divider network 3060, and may also include a frequency sense output such as described above.
The microcontroller 3030 of this embodiment also receives input related to low side current and voltage. Current from the low side may be input through a shunt resistor 3060 having a known resistance, the voltage across this shunt resistor 3060 used to calculate the current provided to the load 3020. Low side voltage is provided from a voltage divider network 3070. It is noted that the low side current and voltage sense signals are not isolated signals, as these signals in this embodiment have relatively low voltage levels that do not require isolation. It will be understood that necessary isolation may be achieved according to many common methods. The microcontroller 3030 operates to collect information related to the voltage and current inputs and may process and output information in manners such as described above to provide power metrics related to the switch mode power supply 3000. The output from the microcontroller 3030 may be through a communications buss 3080 as illustrated in
For example, typical power supplies are most efficient, when in good operating order, at a load of 80-90% of standard capacity. In the event that a power supply load is only 60% of capacity, and the load appears static, the power supply could itself adjust internally, based on the load, to be more efficient. Embodiments such as described above can provide the metrics or underlying measurements (e.g., waveform comparisons) to trigger the adjustment. The power supply can also include a remote reporting capability to report out information.
Additionally, in certain other embodiments, generation of power metrics as described above and internal clocking based on an incoming AC signal, are incorporated into other types of appliances other than computing-related equipment, such as household computer, TV, stereo, and/or other appliances. Such appliances may use the information to adjust internally based on load and/or report out problems, power metrics, etc. Such communications may be through a wired or wireless communications interface to a remote power manager interconnected, for example, to the smart grid. In some embodiments, the power supply calculates only some, or none of the above noted metrics, but uses this type of monitoring to take action.
As shown in
In some embodiments a power distribution unit is adapted for horizontal mounting using appropriate hardware for attachment to a horizontal surface, for example an underside of an upper panel 1829 or between the lower horizontal member 1815 on one side of the rack and a corresponding horizontal member (not shown) on the other side of the rack.
As shown in
In certain embodiments, assets that receive power from a PDU include power supplies having such power measurement and reporting circuitry. The PDU includes a communication interface (wired or wireless) and receives power supply metrics from each unit of supported electronics equipment through the communications link. The PDU can utilize and/or report the metrics to other remote entities.
The phrase “Per Outlet Power Sensing” (“POPS”) refers to the concept of monitoring power consumption at each outlet as discussed above. With an Internet interface, monitoring power consumption at each outlet provides detailed power information and allows grouping of outlets to determine kilowatt consumption per device, group of devices, CDU, or cabinet. Power consumption can also be determined per rack, rows of racks, an entire data center, or the like by clustering outlet information across multiple IP addresses and CDUs, as discussed above. This can provide consolidated CDU information within a data center or across multiple locations, a centralized location to view power and environmental status, capacity planning, reports and trends, multiple views, auto discovery of all CDU devices, alarm details, an ability to manage CDUs, global or individual outlet control, and logging.
In can thus be seen that embodiments provide a number of novel features and advantages including, for example: (a) sensing and output of information related to the current and voltage output to various different components and/or applications; (b) an AC input clock compensation solution integral to a microcontroller, in which a power monitoring circuit and/or power meter does not require an external oscillator for a time base; (c) predictive failure of various power components; (d) an accurate energy accumulation scheme for one or more outputs associated with a single power monitoring and metering circuit; (d) output switching capability with relatively low power requirements using switching versus holding transistors in relay circuits used to switch the outputs; (e) output switching at zero voltage crossings in the AC power cycle; (f) modular construction of an outlet assembly with options to provide switched outputs or non-switched outputs; (g) the ability to determine if lack of power at an outlet is the result of loss of input power or a blown fuse and (h) the ability to assess the health of power supplies in an installed base of power supplies in data center equipment racks without requiring any modification of the power supplies.
From the foregoing, it will be appreciated that specific embodiments of the invention have been described herein for purposes of illustration, but that various modifications may be made without deviating from the scope of the invention. Accordingly, the invention is not limited except as by the appended claims.
Claims
1. A power distribution unit comprising:
- a power distribution unit housing disposable in an electrical equipment rack of the type in which a plurality of electrical components are removably mountable;
- a power input penetrating the housing;
- a voltage sensor;
- a plurality of power outputs disposed in the housing, each in electrical communication with the power input and each connectable to an electrical load;
- a plurality of current sensors each in electrical communication with one of the power outputs to sense current through each of the plurality of the power outputs, the plurality of current sensors disposed within the housing; and
- a power monitoring section in electrical communication with the voltage sensor and the current sensors and responsive to signals provided by the sensors to (1) sample the signals to obtain samples of voltage and current at each of the plurality of power outputs during one cycle of input power, (2) calculate raw RMS values of voltage and current from the samples, and (3) scale the raw RMS values according to a predetermined calibration factor to obtain corrected RMS voltage and current values for the load connected to each power output.
2. A power distribution unit as in claim 1 wherein the power distribution unit housing is adapted for mounting within an electrical equipment rack in a vertical orientation.
3. A power distribution unit as in claim 1 and further comprising a numeric display.
4. A power distribution unit as in claim 3 wherein the voltage sensor, the current sensors, the numeric display and the power monitoring section are disposed in the power distribution unit housing.
5. A power distribution unit as in claim 1 wherein the power monitoring section stores the samples of voltage and current.
6. A power distribution unit as in claim 1 wherein the power monitoring section stores the corrected RMS voltage and current values.
7. A power distribution unit as in claim 1 wherein the power monitoring section calculates for each load at least one of average active power, average apparent power, power factor, and input current crest factor.
8. A power distribution unit as in claim 1 wherein the power monitoring section calculates a phase angle between the voltage across and the current flowing through each load.
9. A power distribution unit as in claim 1 wherein the power monitoring section calculates energy consumed over an interval longer than one cycle of input power by each load.
10. A power distribution unit as in claim 1 wherein the power monitoring section comprises an analog-to-digital converter (ADC) in electrical communication with the voltage sensor and the current sensors, processing logic in electrical communication with the ADC, and a memory in electrical communication with the processing logic.
11. A power distribution unit as in claim 10 wherein samples of voltage and current obtained over more than one cycle of input power are stored in the memory.
12. A power distribution unit as in claim 11 wherein the processing logic compares samples of voltage and current obtained with respect to one of the loads during a first voltage cycle with samples of voltage and current obtained with respect to the same load during a second voltage cycle and generates an alert signal if there is a difference of predetermined magnitude therebetween.
13. A power distribution unit as in claim 10 and further comprising, stored in the memory, model samples of voltage and current representing one of the loads.
14. A power distribution unit as in claim 13 wherein the processing logic compares the model samples with samples obtained with respect to the same load during a voltage cycle and generates an alert signal if there is a difference of predetermined magnitude therebetween.
15. A power distribution unit as in claim 1 and further comprising a timing sensor in electrical communication with the power input and the power monitoring section.
16. A power distribution unit as in claim 15 wherein the power monitoring section is responsive to the timing sensor to calculate a frequency of the input power.
17. A power distribution unit as in claim 16 wherein the power monitoring section uses the calculated frequency to compensate for errors in an internal processor time base.
18. A power distribution unit as in claim 15 wherein the power monitoring section is responsive to the timing sensor to calculate a reload value and to use the reload value to determine sampling intervals for sampling the voltage and current.
19. A power distribution unit as in claim 1 and further comprising a communication section for establishing communication between the power monitoring section and a remotely located network power manager.
20. A power distribution unit comprising:
- a power distribution unit housing disposable in an electrical equipment rack in which a plurality of electrical components are removably mountable;
- a power input penetrating the housing;
- a plurality of power outputs disposed in the housing to distribute power to the plurality of electrical components;
- a voltage sensor communicable with the power outputs;
- a plurality of current sensors each communicable with one of the power outputs to detect current flow through each of the power outputs;
- a processor disposed in the housing and communicably coupled to the voltage sensor and to the plurality of current sensors; and
- a memory associated with the processor and configured to store at least one of: historic voltage waveform data, historic current waveform data, and historic power metric data other than the historic voltage waveform data and historic current waveform data, the processor configured to determine or receive a corresponding at least one of: present voltage waveform data from the voltage sensor, present current waveform data from the current sensors, and present power metric data other than the present voltage waveform data and the present current waveform data, the processor configured to compare at least one of: magnitudes of the historic voltage waveform data to magnitudes of the present voltage waveform data, magnitudes of the historic current waveform data to magnitudes of the present current waveform data, and the historic power metric data to the present power metric data, wherein the historic voltage waveform data and the historic current waveform data exclude the present voltage waveform data and the present current waveform data, wherein the processor generates a notification if the voltage comparisons, the current comparisons, or the other power metric comparisons exceed associated predetermined thresholds.
21. A power distribution unit as in claim 20 and further comprising a storage unit communicable with the processor.
22. A power distribution unit as in claim 20 wherein the power distribution unit housing is adapted for mounting within an electrical equipment rack in a vertical orientation.
23. A power distribution unit as in claim 20 and further comprising a numeric display.
24. A power distribution unit as in claim 23 wherein the voltage sensor, the current sensors, and the numeric display are disposed in the power distribution unit housing.
25. A power distribution unit as in claim 20 wherein the historic and present power metric data include one or more of: an RMS calculation, an average active power calculation, an average apparent power calculation, a power factor calculation, an input current crest factor calculation, a voltage-to-current phase angle calculation, and an energy usage calculation.
26. A power distribution unit as in claim 20 wherein the processor comprises an analog-to-digital converter and an arithmetic logic unit.
27. A power distribution unit as in claim 20 and further comprising a timing sensor communicable with the power input.
28. A power distribution unit as in claim 20 and further comprising a communication section communicable with the processor and with a communication network external of the housing.
29. A method of managing a plurality of electrical loads each drawing electrical power from a power distribution unit, the method comprising:
- sampling, with a plurality of sensors disposed within the power distribution unit, voltage across and current flowing through each of the loads repeatedly during one cycle of input power;
- calculating, with a processor disposed within the power distribution unit, raw RMS values of voltage and current from the samples;
- scaling, with the processor, the raw RMS values according to a predetermined calibration factor to obtain corrected RMS voltage and current values for each of the loads;
- storing model samples of voltage and current representative of one of the loads;
- comparing the stored model samples with samples of voltage and current obtained with respect to the same load during the one cycle of input power; and
- generating an alert signal if there is a difference of a predetermined magnitude therebetween.
30. A method as in claim 29 and further comprising storing the samples of voltage and current.
31. A method as in claim 30 wherein storing the samples comprises storing samples of voltage and current obtained over more than one voltage cycle.
32. A method as in claim 29 and further comprising storing the corrected RMS voltage and current values.
33. A method as in claim 29 and further comprising calculating for each load at least one of average active power, average apparent power, power factor, input current crest factor, phase angle between voltage across and current flowing through the load, and energy consumed over an interval longer than one cycle of input power by the load.
34. A method as in claim 29 and further comprising:
- comparing samples of voltage and current obtained with respect to one of the loads during a first voltage cycle with samples of voltage and current obtained with respect to the same load during a second voltage cycle; and
- generating an alert signal if there is a difference of predetermined magnitude therebetween.
35. A method as in claim 29 and further comprising sensing a zero crossing of a cycle of input power.
36. A method as in claim 35 and further comprising calculating a frequency of the input power.
37. A method as in claim 36 and further comprising compensating an internal time base according to the frequency.
38. A method as in claim 35 and further comprising calculating a reload value; and determining sampling intervals for sampling the voltage and current according to the reload value.
39. A method as in claim 29 and further comprising communicating the corrected RMS voltage and current values to a remotely located network power manager.
40. A power distribution unit as in claim 1 wherein the power distribution unit housing is adapted for mounting within an electrical equipment rack in a horizontal orientation.
41. A power distribution unit as in claim 20 wherein the power distribution unit housing is adapted for mounting within an electrical equipment rack in a horizontal orientation.
Type: Application
Filed: Apr 8, 2014
Publication Date: Aug 7, 2014
Patent Grant number: 9952261
Applicant: SERVER TECHNOLOGY, INC. (Reno, NV)
Inventors: Carrel W. Ewing , James P. Maskaly (Sparks, NV), Brian P. Auclair (Reno, NV), Dennis W. Mcglumphy (Sun Valley, NV)
Application Number: 14/247,900
International Classification: G01R 21/10 (20060101); G01R 21/00 (20060101); G01R 35/00 (20060101); H02B 1/01 (20060101);